Heba ate $\dfrac{1}{12}$ of a box of cereal. Now the box is $\dfrac{3}{4}$ full. What fraction of a full box was there before Heba ate?
Heba ate ${\dfrac{1}{12}}$ of a box of cereal and there is $\dfrac{3}{4}}$ of a box left. $\frac{1}{12}$ $\frac{3}{4}$ amount of cereal to start cereal eaten amount of cereal now ${\dfrac{1}{12}}+\dfrac{3}{4}} = {\text{ amount of cereal to start}}$ Our denominators need to be the same so we can add. What is the least common multiple for the denominators ${12}$ and $4}$ ? The least common multiple of ${12}$ and $4}$ is ${12}$. $\dfrac{3}\times 3}{4}\times 3} = \dfrac{9}{12}}$ Now, we can add our fractions. ${\dfrac{1}{12}} + \dfrac{9}{12}} = \dfrac{{1} + 9}}{12} ={\dfrac{10}{12}}$ There was $\dfrac{10}{12}$ of a box of cereal before Heba ate. This answer can also be written as $\dfrac{5}{6}$ of a box.